1. Field of the Invention
The present invention relates to a method for referencing fixed objects on the surface of the earth by associating an unambiguous code.
2. Description of the Prior Art
Many traffic-telematic services presuppose the transmitting of information to a final instrument. Such a final instrument may, for instance, be installed in a vehicle or may be a portable instrument. The information is ordinarily provided by a central service station or a system of service stations. A large part of the information to be transmitted refers in this connection to geographical positions. Typical examples of this are any type of traffic information. It is therefore necessary that the position information transmitted be correctly associated so that the traffic information can be meaningfully used.
For the unambiguous associating of position data with fixed objects, which is also referred below to as referencing, various solutions are known and used in technical systems. The disadvantages of existing systems will be explained on a suitable example. Thus, in the so-called RDS/TMC system (Radio-Data System/Traffic Message Channel) traffic information is coupled to a hierarchically structured model (in accordance with location codes of the Alert-C Protocol) of the network of roads. A predefined network of roads is in this connection broken down into road sections and numbered consecutively. By definition of higher-order and lower-order sections a hierarchic structure is established. Thus, for instance, the entire length of Autobahn A 57 represents a section of higher order and for instance the stretch of A 57 between the Strumpp intersection and the Krefeld-Oppum exit or between the Kaarst intersection and the Neuss-Buttgen exit represent sections of lower order. Such individual sections can then be simply numbered consecutively, as shown in FIG. I for a portion of a map. Information is then transmitted in each case with reference to the number of the previously defined section. Such a method has the advantage of a minimal volume of data for the referencing upon the transmission of information.
A decisive disadvantage of this and many other methods is that the transmission of the information is dependent on the reference model (in this case, on the predetermined structure of the road network) and this reference model must be known also in the corresponding end instrument located at the user in order that the information can be understood correctly. A refining of the model is generally not possible. Different geographical models (for instance road maps of different manufacturers) cannot be used because of the different structure. Upon change of the structure, the presentation of the data becomes increasingly chaotic so that problems of compatibility can occur both between different end instruments and between different generations of the data structure.
Another known solution consists of coupling the referencing not with traffic-relevant structures such as, for instance, consecutively numbered road sections, but to use directly geodetic coordinates, as shown diagrammatically in FIG. 2. In technical use, the WGS-84 format (World Geodetic System) would, for instance offer itself here, in the same way as it is also used in the ordinary satellite navigation systems (GPS receivers). One disadvantage of this is that certain traffic-telematic applications, such as for instance navigation on large complicated intersections, require very high resolution and the available data material which is used by different manufacturers is in each case consistent only in itself. Upon the referencing of traffic objects, there are greater or lesser differences depending on the data material used, and thus problems of compatibility arise in the use of traffic-telematic services. An intersection, to be sure, is an intersection both on a map of manufacturer A and on one of manufacturer B, but the rule is that in each case there are associated with this intersection WGS coordinates which frequently differ from each other by up to 100 meters. The use of such coordinates, therefore, does not permit an association which is unambiguous for all manufacturers.
A further source of ambiguities and problems in association results from the description of larger complex objects by differently structured objects of lower order (reference elements). One example of this is an autobahn or expressway intersection with several entrances and exits (reference elements).